gravel road and parking lot in Montana

[jpeter2406]

I am trying to build a gravel road and gravel parking lot in Montana in the least expensive way. The soil is a hard clay. Does anyone have any suggestions on the design and type of gravel, etc?

Thanks
John

 

[KRSServices]

Ensure the parking area and road are well drained. I would also suggest proofrolling the road subgrade and provide for a lift of at least 50 mm of traffic gravel stabilized with a suitable binder. This will not only keep the gravels on the roadway for strength, but also suppress dust as well. Many other factors will come into play here, but as a general comment, this should give you a relatively trouble free road. If the road is to be subjected to heavy loading, then some additional work is necessary to keep it from costing a small fortune in future maintenance costs. I provide these kinds of roads to oilfield clientele (roads and padsites) so this idea could be considered in your appication.

KRS Services

http://www.krs-services.com

 

[jpeter2406]

Thanks for your input on my road project in Montana. I have been looking into the options of laying down a geo-textile first and using 4-6 inches of road mix gravel on top of that. What do you think of this approach? The geo-textile I have been looking at is from SI Geosolutions.

Thanks
John

 

[Focht3]

I have mixed feelings.

The geotextile will separate the gravel from the soil - provided that it is not a woven product on clay or silt soils. It will also provide some tensile reinforcement where it is needed most.

But the absence of anything to "hold" the gravel together concerns me. Four to six inches of road mix gravel could easily be three inches in some areas. That's not enough cover to either protect the geotextile or provide a pavement "structure" where the geotextile and gravel work together. This concern is really a maintenance issue; maintain the drive and you shouldn't have too many problems.

 

[KRSServices]

I think that you are wasting your money by purchasing and placing the geotextile. First of all you are constructing a gravel road. You stated that the clay soil is hard, so I'm going to assume that will suffice as a good subgrade material. Determine the typical loading the road will be subjected too and design accordingly. Ensure that the grade is constructed well above the ditchline and that your borrow material is free from unsuitable ond organic soils. Properly strip the right of way and prep the native soils. Build the grade and ensure even compaction throughout. Final grading is important to ensure that water will shed properly and proof roll to verify that the subgrade is firm and does not deflect. Place the gravel on top. Unless you are going to stabilize or "glue" the gravels together or finish with ACP or asphalt stabilized base course, 4" will quickly be lost to the ditch and shoulders. Maintain frequently, which will be evident because while this road is cheap to construct, it is high maintenance. Same goes for the parking lot, except, drainage is going to be key, particularly in the spring when the ground thaws. Depressions and areas of ponding will quickly become rutted and a muddy mess if not properly maintained.

KRS Services

http://www.krs-services.com

 

[SirAl]

The term 'Hard Clay' concerns me somewhat. I have seen a number of hard, dry, clay subgrades turn soft and problematic when exposed to rainfall. It is important to provide adequate moisture treatment and recompaction to dry clays during the roadbed construction. Adequate cross drainage of the road top as well as positive ditch drainage is also important. The filter cloth, for this application, is of little benefit. The 6 inches of gravel thickness that you referred to is excessive in my view. Even with well compacted open gravel structures, the gravel will ravel under traffic. Befor you know it, an abundance of the gravel will find its way to the shoulder of the road, hindering surface drainage. A thinner gravel structure, 3 inches or so, is more like it. A 1 inch crush surfacing gravel with reasonable fracture, would be a good product. As with all gravel roads, regular grader work with periodic applications of additional gravel will be required.

 

[KRSServices]

John,

What did you decide to do? I'm just curious.

KRS Services

http://www.krs-services.com

 

[dirtsqueezer]

jpeter2406,

I agree with Focht3 and SirAl. My experience is that geotextile fabric is used to bridge soft areas of your parking lot, but in order to do this, you need more than 50mm of fill. I've used Mirafi in the same situation, for which at least 18" of fill is recommended for proper stabilization. The reasoning has been to me as a 'trampoline' effect; the fill surrounding the soft area will hold the fabric taught, minimizing movement of the ashpalt on top of it. But you need enough fill to 'pin' that fabric at the edges, giving it the holding power to bridge the soft area.

I would get a loaded gravel or water truck and roll it across your clay. If you were able to get a look at it last winter/spring during the rainy season, I'd use that information as well. If that clay base moves enough to worry you, I would overexcavate 18", lay down the fabric, followed by 18" of fill, your crushed layer, then pave. If you do a proof roll feel that all of that work would just be rediculous, I would just pave as-is, with the 2" lift of crushed rock, with maybe and inch or so more asphalt just to be sure.


Best of luck! Let us know how it went.

 

[Zambo]

This is a very interesting topic, but I guess the road/parking lot has now been constructed.

I would use a geotextile of the geogrid type (as Focht3 states a woven product is not required here) If the clay is a hard clay a geogrid membrane will separate the materials and reduce the thickness of fill required.

Next I would place a 3" clean crushed limestone layer, as thick as the construction budget will allow. Best if this is 12" thick and as single sized as possible,if not as thick as can be afforded. After this continue to compact with a vibratory roller and spread crushed rock fines. On top your gravel surfacing couple of inches thick.

Of course drainage is the key and falls should be to open ditches which are well maintained.

Zambo